This invention relates in general to a sail batten construction and a method of manufacturing it, and more particularly to an elongated sail batten structure formed of a fiber reinforced thermoplastic composite material, characterized by a varying stiffness profile along its length.
Sail battens are stiffening elements positioned within pockets or otherwise positioned at the surface of a sail to maintain its airfoil shape under a variety of wind conditions. In its most simple form the batten is an elongated structural member of generally uniform cross sectional dimensions along its length and may be formed of any of a variety of materials exhibiting appropriate strength to weight characteristics. Battens in the past have been formed of wood, fiberglass, and other fiber reinforced composite materials. The airfoil shape desired for the sail includes a curve in the forward section of the sail moving out to a relatively flat section toward the leech of the sail. Ideally, then, the batten should have a variable bending stiffness along its length.
Battens have been formed as solid straight rods which, while strong and inexpensive, have a constant transverse stiffness characteristic over their length and are relatively heavy. Such a solid batten may also have one end ground to a taper, thereby improving the shape characteristic and reducing the weight somewhat, but with a resultant loss of strength. Battens formed of laminated material can be used in a tapered structure exhibiting varying transverse stiffness characteristics along their length. However, laminated structures are expensive to produce.
Similarly the basic construction of a batten may be a hollow tube, rather than a solid rod. A tapering tube is very expensive to produce and straight tubes do not have the desired varying transverse stiffness profile along the length.
It is therefore an object of the present invention to provide a batten formed of a fiber reinforced composite material and having a suitable strength weight characteristic which can be economically produced with a varying transverse stiffness profile over the length of the batten.
Another object of this invention is to provide a method for manufacturing a sail batten of composite material in a first step and thereafter, in a second step, secondary processing that tube to vary its transverse stiffness characteristic along the length of the batten.
It is yet another object of this invention to form a sail batten of a fiber reinforced composite material having a varying transverse stiffness profile along its length, where the stiffness profile is suitable to meet specific airfoil characteristics.